The work in the second year of the project will include the area of RIA analysis of estradiol and progesterone, both of cycling control hamsters and of samples taken from hamsters which have received optimal sc doses of tetrapeptide for four and eight days (one and two cycles). Both the protein "carrier" from plasma and the "storage" protein will be studied as to binding capability with the tetrapeptide. Attempts will be made to determine charge of the proteins, with and without the tetrapeptide. It is hoped that the low activity of some synthetic samples may be explained on the basis of specificity of the proteins. Sufficient "steroid" is being accumulated so that a structural analysis may be attempted on that material from the stroma of the oviduct. Finally, the tripeptide, resulting from tryptic digestion of the tetrapeptide (removal of terminal lysine) will be obtained locally and tested orally for biological effect.